Metrohm NIRS XDS MasterLab Analyzer - Manual (Page 102)

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The view above shows Transmission gain on a typical MasterLab Analyzer. The gain program
measures amplifier gain factor and voltage through the Tablet Transmission Reference. Gain is
reported for NIR, since this detector does not provide separate voltages. While VIS gain is reported, it
is a function of NIR gain and can be ignored.
Gain Factor is a measure of signal amplification. Gain ranges from about 4000 to 400,000 in normal
use.
Gain Adjust can be helpful when troubleshooting an instrument. For example, a gain of 400,000 in
NIR may indicate a blocked beam, or a detector not in the proper position.
Note that the gain factors are reported in Performance Test, and can be called up from the
Diagnostic Database. This permits the user to see if the gain factor has changed significantly over
time.
7.2.5 Low Flux Test
Low Flux Test is included for users who wish to run this test in support of regulatory
recommendations (Note that USP has not defined tests on high-absorbance transmission instruments
of this type [as of this document release]; therefore this test is optional.)
Low Flux Test uses an internal 10% neutral density (transmittance) screen, triggered by software, and
combined with the Tablet Transmission Reference, to provide an AU value of about 3 AU. A noise
test is run using this standard. Because the transmission value is considerably less than that of the
instrument standard, the test is considered a good method for testing instrument noise in the range
of transmission of many common tablet sample absorptions.
To initiate the Low Flux Test, follow this sequence: